Transmission is also called

• A. Transmission Gear Box
• B. Main Gear Box
• C. Driveshaft Assembly
• D. Rotor Drive Unit

Answer: (B)

The key idea here is the component that takes power from the engine and delivers it to the rotor while changing the speed — that's the main gear box. In rotorcraft, this unit is the central gear reduction and power-transmission assembly, so it’s commonly called the main gear box. It houses the gears and shafts that reduce the engine RPM to the rotor RPM and transfer torque to the rotor drive system.

The other terms aren’t the standard name for this function. A driveshaft assembly is mainly the shaft network that carries power between components, not the gear reduction unit itself. A rotor drive unit refers to the broader drive system including the rotor mast and related parts, not specifically the gearbox. And while you might see “transmission” used in some contexts, the rotorcraft-specific and widely accepted term for this assembly is the main gear box.